Over 50 per cent of participants in the University of Texas M. D. Anderson Cancer Center study experienced a clinical response to the green tea extracts, according to findings published in Cancer Prevention Research.

“While still very early, and not definitive proof that green tea is an effective preventive agent, these results certainly encourage more study for patients at highest risk for oral cancer,” explained the research team.

“The extract’s lack of toxicity is very crucial in prevention trials. It’s very important to remember that these are otherwise healthy individuals and we need to ensure that agents studied produce no harm,” they added.

Green tea contains between 30 and 40 per cent of water-extractable polyphenols, while black tea (green tea that has been oxidized by fermentation) contains between 3 and 10 per cent. Oolong tea is semi-fermented tea and is somewhere between green and black tea.

The four primary polyphenols found in fresh tealeaves are epigallocatechin gallate (EGCG), epigallocatechin (EGC), epicatechin gallate (ECG), and epicatechin (EC).

The study followed 41 people with oral leukoplakia, a condition is a sign of oral cancer risk. The participants were assigned to receive either placebo or green tea extract at one of three doses, including 500 milligrams or 1,000 mg three times a day.

The researchers collected oral tissue biopsies, which they say was “essential in that it allowed us to learn that not only did the green tea extract appear to have benefit for some patients, but we pointed to anti-angiogenic effects as a potential mechanism of action,” they explained.

Almost 60 per cent of people taking the two highest doses of the green tea extracts had a clinical response. Just over 36 per cent of people in the lowest extract dose group had a clinical response, compared to 18 per cent in the placebo group, said the researchers.

At an extended follow-up with a mean of 27.5 months, 15 participants had developed oral cancer, with a median time to disease development of 46.4 months.

Commenting on the safety, the researchers noted that side effects such as insomnia and nervousness were mostly only recorded in the high-dose group. None of these produced no significant toxicity, they added.

“While these are encouraging findings, much more research must be done before we can conclude that green tea may prevent oral or any other type of cancer. It’s also important to remind people that this trial enrolled very few participants who, at the highest dose levels took the equivalent of eight cups of green tea three times a day,” cautioned the researchers.

“We need to further understand if green tea offers longer-term prevention effects for patients,” they added. Future studies with such high-risk people investigate the effects of longer supplementation periods, said the researchers.

According to the American Cancer Society, more than 35,720 are expected to be diagnosed with oral and/or pharynx cancer and the five year survival rate is less than 50 per cent.